unbranded means no manufacturer stated at the top of the disc so on the top there isn't anything printed. Nice when you use a CD-R printer to print your own logo's and Mitsui is one of the compannies that does this. These are good discs.(Maybe even better as Taiyo Yuden because of the better compatibility in players.)

High c1 errors depends from disc to disc. Some discs can handle higher speeds very good but this depends on the discs. But on some discs you will get very high c1 errors.